The current trend is to use language-oriented package manager, such as npm or bower for javascript, pip for python, gems for ruby and so on.
As I understand the need for a dependency manager when you want to deploy your application (they all can do that). I don’t get it when you need a new package-manager for installing local app on your system. I think you should always rely on your default package manager.
Why some tools are only distributed with pip, or npm and not with system package manager as apt, rpm, or yum ?